Network Working Group A. Barbir
Request for Comments: 3835 R. Penno
Category: Informational Nortel Networks
R. Chen
AT&T Labs
M. Hofmann
Bell Labs/Lucent Technologies
H. Orman
Purple Streak Development
August 2004
An Architecture for Open Pluggable Edge Services (OPES)
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This memo defines an architecture that enables the creation of an
application service in which a data provider, a data consumer, and
zero or more application entities cooperatively implement a data
stream service.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 . The Architecture . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. OPES Entities. . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Data Dispatcher. . . . . . . . . . . . . . . . . 5
2.2. OPES Flows . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. OPES Rules . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Callout Servers. . . . . . . . . . . . . . . . . . . . . 7
2.5. Tracing Facility . . . . . . . . . . . . . . . . . . . . 8
3. Security and Privacy Considerations . . . . . . . . . . . . . 9
3.1. Trust Domains. . . . . . . . . . . . . . . . . . . . . . 9
3.2. Establishing Trust and Service Authorization . . . . . . 11
3.3. Callout Protocol . . . . . . . . . . . . . . . . . . . . 11
3.4. Privacy. . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. End-to-end Integrity . . . . . . . . . . . . . . . . . . 12
4. IAB Architectural and Policy Considerations for OPES . . . . . 12
4.1. IAB consideration (2.1) One-party Consent. . . . . . . . 12
4.2. IAB consideration (2.2) IP-Layer Communications. . . . . 13
4.3. IAB consideration (3.1 and 3.2) Notification . . . . . . 13
4.4. IAB consideration (3.3) Non-Blocking . . . . . . . . . . 13
4.5. IAB consideration (4.1) URI Resolution . . . . . . . . . 13
4.6. IAB consideration (4.2) Reference Validity . . . . . . . 13
4.7. IAB consideration (4.3) Application Addressing
Extensions . . . . . . . . . . . . . . . . . . . . . . . 14
4.8. IAB consideration (5.1) Privacy. . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16
11. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 17
1. Introduction
When supplying a data stream service between a provider and a
consumer, the need to provision the use of other application
entities, in addition to the provider and consumer, may arise. For
example, some party may wish to customize a data stream as a service
to a consumer. The customization step might be based on the
customer's resource availability (e.g., display capabilities).
In some cases it may be beneficial to provide a customization service
at a network location between the provider and consumer host rather
than at one of these endpoints. For certain services performed on
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behalf of the end-user, this may be the only option of service
deployment. In this case, zero or more additional application
entities may participate in the data stream service. There are many
possible provisioning scenarios which make a data stream service
attractive. The OPES Use Cases and Deployment Scenarios [1] document
provides examples of OPES services. The document discusses services
that modify requests, services that modify responses, and services
that create responses. It is recommended that the document on OPES
Use Cases and Deployment Scenarios [1] be read before reading this
document.
This document presents the architectural components of Open Pluggable
Edge Services (OPES) that are needed in order to perform a data
stream service. The architecture addresses the IAB considerations
described in [2]. These considerations are covered in various parts
of the document. Section 2.5 addresses tracing; section 3 addresses
security considerations. Section 4 provides a summary of IAB
considerations and how the architecture addresses them.
The document is organized as follows: Section 2 introduces the OPES
architecture. Section 3 discusses OPES security and privacy
considerations. Section 4 addresses IAB considerations for OPES.
Section 5 discusses security considerations. Section 6 addresses
IANA considerations. Section 7 provides a summary of the
architecture and the requirements for interoperability.
2. The Architecture
The architecture of Open Pluggable Edge Services (OPES) can be
described in terms of three interrelated concepts, mainly:
o OPES entities: processes operating in the network;
o OPES flows: data flows that are cooperatively realized by the
OPES entities; and,
o OPES rules: these specify when and how to execute OPES services.
2.1. OPES Entities
An OPES entity is an application that operates on a data flow between
a data provider application and a data consumer application. OPES
entities can be:
o an OPES service application, which analyzes and possibly
transforms messages exchanged between the data provider
application and the data consumer application;
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o a data dispatcher, which invokes an OPES service application based
on an OPES ruleset and application-specific knowledge.
The cooperative behavior of OPES entities introduces additional
functionality for each data flow provided that it matches the OPES
rules. In the network, OPES entities reside inside OPES processors.
In the current work, an OPES processor MUST include a data
dispatcher. Furthermore, the data provider and data consumer
applications are not considered as OPES entities.
To provide verifiable system integrity (see section 3.1 on trust
domains below) and to facilitate deployment of end-to-end encryption
and data integrity control, OPES processors MUST be:
o explicitly addressable at the IP layer by the end user (data
consumer application). This requirement does not preclude a chain
of OPES processors with the first one in the chain explicitly
addressed at the IP layer by the end user (data consumer
application).
o consented to by either the data consumer or data provider
application. The details of this process are beyond the scope of
the current work.
The OPES architecture is largely independent of the protocol that is
used by the data provider application and the data consumer
application to exchange data. However, this document selects HTTP
[3] as the example for the underlying protocol in OPES flows.
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2.1.1. Data Dispatcher
Data dispatchers include a ruleset that can be compiled from several
sources and MUST resolve into an unambiguous result. The combined
ruleset enables an OPES processor to determine which service
applications to invoke for which data flow. Accordingly, the data
dispatcher constitutes an enhanced policy enforcement point, where
policy rules are evaluated and service-specific data handlers and
state information are maintained, as depicted in Figure 1.
+----------+
| callout |
| server |
+----------+
||
||
||
||
+--------------------------+
| +-----------+ || |
| | OPES | || |
| | service | || |
| |application| || |
| +-----------+ || |
| +----------------------+ |
OPES flow | | data dispatcher and | | OPES flow
| | policy enforcement | |
| +----------------------+ |
| OPES |
| processor |
+--------------------------+
Figure 1: Data Dispatchers
The architecture allows for more than one policy enforcement point to
be present on an OPES flow.
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2.2. OPES Flows
An OPES flow is a cooperative undertaking between a data provider
application, a data consumer application, zero or more OPES service
applications, and one or more data dispatchers.
Since policies are enforced by data dispatchers, the presence of at
least one data dispatcher is required in the OPES flow.
data OPES OPES data
consumer processor A processor N provider
+-----------+ +-----------+ . +-----------+ +-----------+
| data | | OPES | . | OPES | | data |
| consumer | | service | . | service | | provider |
|application| |application| . |application| |application|
+-----------+ +-----------+ . +-----------+ +-----------+
| | | | . | | | |
| HTTP | | HTTP | . | HTTP | | HTTP |
| | | | . | | | |
+-----------+ +-----------+ . +-----------+ +-----------+
| TCP/IP | | TCP/IP | . | TCP/IP | | TCP/IP |
+-----------+ +-----------+ . +-----------+ +-----------+
|| || || . || || ||
================ =====.======== ===========
| |
Figure 2: An OPES flow
Figure 2 depicts two data dispatchers that are present in the OPES
flow. The architecture allows for one or more data dispatchers to be
present in any flow.
2.3. OPES Rules
OPES' policy regarding services and the data provided to them is
determined by a ruleset consisting of OPES rules. The rules consist
of a set of conditions and related actions. The ruleset is the
superset of all OPES rules on the processor. The OPES ruleset
determines which service applications will operate on a data stream.
In this model, all data dispatchers are invoked for all flows.
In order to ensure predictable behavior, the OPES architecture
requires the use of a standardized schema for the purpose of defining
and interpreting the ruleset. The OPES architecture does not require
a mechanism for configuring a ruleset into a data dispatcher. This
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is treated as a local matter for each implementation (e.g., through
the use of a text editor or a secure upload protocol), as long as
such a mechanism complies with the requirements set forth in section
3.
2.4. Callout Servers
The evaluation of the OPES ruleset determines which service
applications will operate on a data stream. How the ruleset is
evaluated is not the subject of the architecture, except to note that
it MUST result in the same unambiguous result in all implementations.
In some cases it may be useful for the OPES processor to distribute
the responsibility of service execution by communicating with one or
more callout servers. A data dispatcher invokes the services of a
callout server by using the OPES callout protocol (OCP). The
requirements for the OCP are given in [5]. The OCP is application-
agnostic, being unaware of the semantics of the encapsulated
application protocol (e.g., HTTP). However, the data dispatcher MUST
incorporate a service aware vectoring capability that parses the data
flow according to the ruleset and delivers the data to either the
local or remote OPES service application.
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The general interaction situation is depicted in Figure 3, which
illustrates the positions and interaction of different components of
OPES architecture.
+--------------------------+
| +-----------+ |
| | OPES | |
| | service | | +---------------+ +-----------+
| |application| | | Callout | | Callout |
| +-----------+ | | Server A | | Server X |
| || | | +--------+ | | |
| +----------------------+ | | | OPES | | | |
| | data dispatcher | | | | Service| | | +--------+|
| +----------------------+ | | | Appl A | | | | OPES ||
| || || | | +--------+ | | |Service ||
| +---------+ +-------+ | | || | | | Appl X ||
| | HTTP | | | | | +--------+ | ... | +--------||
| | | | OCP |=========| | OCP | | | || |
| +---------+ +-------+ | | +--------+ | | +------+ |
| | | || | +---------------+ | | OCP | |
| | TCP/IP | =======================================| | |
| | | | | +------+ |
| +---------+ | +-----------+
+--------||-||-------------+
|| ||
+--------+ || || +--------+
|data |== =========================================|data |
|producer| |consumer|
+--------+ +--------+
Figure 3: Interaction of OPES Entities
2.5. Tracing Facility
The OPES architecture requires that each data dispatcher provides
tracing facilities that allow the appropriate verification of its
operation. The OPES architecture requires that tracing be feasible
on the OPES flow, per OPES processor, using in-band annotation. One
of those annotations could be a URI with more detailed information on
the OPES services being executed in the OPES flow.
Providing the ability for in-band annotation MAY require header
extensions on the application protocol that is used (e.g., HTTP).
However, the presence of an OPES processor in the data request/
response flow SHALL NOT interfere with the operations of non-OPES
aware clients and servers. Non-OPES clients and servers need not
support these extensions to the base protocol.
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OPES processors MUST obey tracing, reporting, and notification
requirements set by the center of authority in the trust domain to
which an OPES processor belongs. As part of these requirements, the
OPES processor may be instructed to reject or ignore such
requirements that originate from other trust domains.
3. Security and Privacy Considerations
Each data flow MUST be secured in accordance with several policies.
The primary stakeholders are the data consumer and the data provider.
The secondary stakeholders are the entities to which they may have
delegated their trust. The other stakeholders are the owners of the
callout servers. Any of these parties may be participants in the
OPES flow.
These parties MUST have a model, explicit or implicit, describing
their trust policy, which of the other parties are trusted to operate
on data, and what security enhancements are required for
communication. The trust might be delegated for all data, or it
might be restricted to granularity as small as an application data
unit.
All parties that are involved in enforcing policies MUST communicate
the policies to the parties that are involved. These parties are
trusted to adhere to the communicated policies.
In order to delegate fine-grained trust, the parties MUST convey
policy information by implicit contract, by a setup protocol, by a
dynamic negotiation protocol, or in-line with application data
headers.
3.1. Trust Domains
The delegation of authority starts at either a data consumer or data
provider and moves to more distant entities in a "stepwise" fashion.
Stepwise means A delegates to B, and B delegates to C, and so forth.
The entities thus "colored" by the delegation are said to form a
trust domain with respect to the original delegating party. Here,
"Colored" means that if the first step in the chain is the data
provider, then the stepwise delegation "colors" the chain with that
data "provider" color. The only colors defined are the data
"provider" and the data "consumer". Delegation of authority
(coloring) propagates from the content producer start of authority or
from the content consumer start of authority, which may be different
from the end points in the data flow.
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Figure 4 illustrates administrative domains, out-of-band rules, and
policy distribution.
provider administrative domain consumer administrative domain
+------------------------------+ +-------------------------------+
| +--------------+ | | +--------------+ |
| |Provider | |Consumer | |
| |Administrative|~~>~~~: policies and ~ |
Figure 4: OPES administrative domains and policy distribution
In order to understand the trust relationships between OPES entities,
each is labeled as residing in an administrative domain. Entities
associated with a given OPES flow may reside in one or more
administrative domains.
An OPES processor may be in several trust domains at any time. There
is no restriction on whether the OPES processors are authorized by
data consumers and/or data providers. The original party has the
option of forbidding or limiting redelegation.
An OPES processor MUST have a representation of its trust domain
memberships that it can report in whole or in part for tracing
purposes. It MUST include the name of the party that delegated each
privilege to it.
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3.2. Establishing Trust and Service Authorization
The OPES processor will have a configuration policy specifying what
privileges the callout servers have and how they are to be
identified. OPES uses standard protocols for authentication and
other security communication with callout servers.
An OPES processor will have a trusted method for receiving
configuration information, such as rules for the data dispatcher,
trusted callout servers, primary parties that opt-in or opt-out of
individual services, etc.
Protocol(s) for policy/rule distribution are out of scope for this
document, but the OPES architecture assumes the existence of such a
mechanism.
Requirements for the authorization mechanism are set in a separate
document [4].
Service requests may be done in-band. For example, a request to
bypass OPES services could be signalled by a user agent using an HTTP
header string "Bypass-OPES". Such requests MUST be authenticated.
The way OPES entities will honor such requests is subordinate to the
authorization policies effective at that moment.
3.3. Callout Protocol
The determination of whether or not OPES processors will use the
measures that are described in the previous section during their
communication with callout servers depends on the details of how the
primary parties delegated trust to the OPES processors and the trust
relationship between the OPES processors and the callout server.
Strong authentication, message authentication codes, and encryption
SHOULD be used. If the OPES processors are in a single
administrative domain with strong confidentiality and integrity
guarantees, then cryptographic protection is recommended but
optional.
If the delegation mechanism names the trusted parties and their
privileges in some way that permits authentication, then the OPES
processors will be responsible for enforcing the policy and for using
authentication as part of that enforcement.
The callout servers MUST be aware of the policy governing the
communication path. They MUST not, for example, communicate
confidential information to auxiliary servers outside the trust
domain.
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A separate security association MUST be used for each channel
established between an OPES processor and a callout server. The
channels MUST be separate for different primary parties.
3.4. Privacy
Some data from OPES flow endpoints is considered "private" or
"sensitive", and OPES processors MUST advise the primary parties of
their privacy policy and respect the policies of the primary parties.
The privacy information MUST be conveyed on a per-flow basis. This
can be accomplished by using current available privacy techniques
such as P3P [7] and HTTP privacy capabilities.
The callout servers MUST also participate in the handling of private
data, they MUST be prepared to announce their own capabilities, and
enforce the policy required by the primary parties.
3.5. End-to-End Integrity
Digital signature techniques can be used to mark data changes in such
a way that a third-party can verify that the changes are or are not
consistent with the originating party's policy. This requires an
inline method to specify policy and its binding to data, a trace of
changes and the identity of the party making the changes, and strong
identification and authentication methods.
Strong end-to-end integrity can fulfill some of the functions
required by "tracing".
4. IAB Architectural and Policy Considerations for OPES
This section addresses the IAB considerations for OPES [2] and
summarizes how the architecture addresses them.
4.1. IAB Consideration (2.1) One-Party Consent
The IAB recommends that all OPES services be explicitly authorized by
one of the application-layer end-hosts (that is, either the data
consumer application or the data provider application).
The current work requires that either the data consumer application
or the data provider application consent to OPES services. These
requirements have been addressed in sections 2 (section 2.1) and 3.
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4.2. IAB Consideration (2.2) IP-Layer Communications
The IAB recommends that OPES processors must be explicitly addressed
at the IP layer by the end user (data consumer application).
This requirement has been addressed in section 2.1, by the
requirement that OPES processors be addressable at the IP layer by
the data consumer application.
4.3. IAB Consideration (3.1 and 3.2) Notification
The IAB recommends that the OPES architecture incorporate tracing
facilities. Tracing enables data consumer and data provider
applications to detect and respond to actions performed by OPES
processors that are deemed inappropriate to the data consumer or data
provider applications.
Section 3.2 of this document discusses the tracing and notification
facilities that must be supported by OPES services.
4.4. IAB Consideration (3.3) Non-Blocking
The OPES architecture requires the specification of extensions to
HTTP. These extensions will allow the data consumer application to
request a non-OPES version of the content from the data provider
application. These requirements are covered in Section 3.2.
4.5. IAB Consideration (4.1) URI Resolution
This consideration recommends that OPES documentation must be clear
in describing OPES services as being applied to the result of URI
resolution, not as URI resolution itself.
This requirement has been addressed in sections 2.5 and 3.2, by
requiring OPES entities to document all the transformations that have
been performed.
4.6. IAB Consideration (4.2) Reference Validity
This consideration recommends that all proposed services must define
their impact on inter- and intra-document reference validity.
This requirement has been addressed in section 2.5 and throughout the
document whereby OPES entities are required to document the performed
transformations.
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4.7. IAB Consideration (4.3) Application Addressing Extensions
This consideration recommends that any OPES services that cannot be
achieved while respecting the above two considerations may be
reviewed as potential requirements for Internet application
addressing architecture extensions, but must not be undertaken as ad
hoc fixes.
The current work does not require extensions of the Internet
application addressing architecture.
4.8. IAB Consideration (5.1) Privacy
This consideration recommends that the overall OPES framework must
provide for mechanisms for end users to determine the privacy
policies of OPES intermediaries.
This consideration has been addressed in section 3.
5. Security Considerations
The proposed work has to deal with security from various
perspectives. There are security and privacy issues that relate to
data consumer application, callout protocol, and the OPES flow. In
[6], there is an analysis of the threats against OPES entities.
6. IANA Considerations
The proposed work will evaluate current protocols for OCP. If the
work determines that a new protocol needs to be developed, then there
may be a need to request new numbers from IANA.
7. Summary
Although the architecture supports a wide range of cooperative
transformation services, it has few requirements for
interoperability.
The necessary and sufficient elements are specified in the following
documents:
o the OPES ruleset schema, which defines the syntax and semantics of
the rules interpreted by a data dispatcher; and,
o the OPES callout protocol (OCP) [5], which defines the
requirements for the protocol between a data dispatcher and a
callout server.
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8. References
8.1. Normative References
[1] Barbir, A., Burger, E., Chen, R., McHenry, S., Orman, H., and R.
Penno, "Open Pluggable Edge Services (OPES) Use Cases and
Deployment Scenarios", RFC 3752, April 2004.
[2] Floyd, S. and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC 3238,
January 2002.
[3] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[4] Barbir, A., Batuner, O., Beck, A., Chan, T., and H. Orman,
"Policy, Authorization, and Enforcement Requirements of the Open
Pluggable Edge Services (OPES)", RFC 3838, August 2004.
[5] Beck, A., Hofmann, M., Orman, H., Penno, R., and A. Terzis,
"Requirements for Open Pluggable Edge Services (OPES) Callout
Protocols", RFC 3836, August 2004.
[6] Barbir, A., Batuner, O., Srinivas, B., Hofmann, M., and H.
Orman, "Security Threats and Risks for Open Pluggable Edge
Services (OPES)", RFC 3837, August 2004.
8.2. Informative References
[7] Cranor, L. et. al, "The Platform for Privacy Preferences 1.0
(P3P1.0) Specification", W3C Recommendation 16
http://www.w3.org/TR/2002/REC-P3P-20020416/, April 2002.
9. Acknowledgements
This document is the product of OPES WG. Oskar Batuner (Independent
consultant) and Andre Beck (Lucent) are additional authors that have
contributed to this document.
Earlier versions of this work were done by Gary Tomlinson (The
Tomlinson Group) and Michael Condry (Intel).
The authors gratefully acknowledge the contributions of: John Morris,
Mark Baker, Ian Cooper and Marshall T. Rose.
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10. Authors' Addresses
Abbie Barbir
Nortel Networks
3500 Carling Avenue
Nepean, Ontario K2H 8E9
Canada
Phone: +1 613 763 5229
EMail: abbieb@nortelnetworks.com
Yih-Farn Robin Chen
AT&T Labs - Research
180 Park Avenue
Florham Park, NJ 07932
US
Phone: +1 973 360 8653
EMail: chen@research.att.com
Markus Hofmann
Bell Labs/Lucent Technologies
Room 4F-513
101 Crawfords Corner Road
Holmdel, NJ 07733
US
Phone: +1 732 332 5983
EMail: hofmann@bell-labs.com
Hilarie Orman
Purple Streak Development
EMail: ho@alum.mit.edu
Reinaldo Penno
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821
USA
EMail: rpenno@nortelnetworks.com
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11. Full Copyright Statement
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